Dog heartworm (Dirofilaria immitis) is a parasite which principally affects dogs but also has been shown to infect other animals such as cats, foxes, raccoons, ferrets, and even man. Other species of Dirofilaria infect additional hosts. For example, Dirofilaria filaria causes parasitic disease in sheep; D. viviparus causes parasitic disease in cows.
The life cycle of Dirofilaria is instituted through the bite of a mosquito which had previously bitten an infected animal. The infective larvae remain in the mosquito where they undergo three molts, after which the infective larvae migrate to the mosquitos' proboscis. The larvae are then ready to be transmitted to another host. The entire maturation process in the mosquito takes anywhere from 7-14 days.
The infective larvae enter an animal following the bite of a mosquito and then pass through three additional molts after which the adolescent parasites migrate to the heart where they will undergo final maturation. Approximately 25-37 weeks will normally transpire following infection, either as a result of infected mosquitoes biting a host or due to subcutaneous injection of appropriate larvae into animals, before microfilaria can be detected by microscopy in the blood of animals so infected.
There have been numerous attempts to prepare antigenic material as immunizing agents against Dirofilaria (Otto, in G. J. Jackson et al., Eds, Immunity to Parasitic Animals, Appleton-Century-Crofts, N.Y., pp. 963-980, 1970) reviewed attempts up to that time to immunize dogs against D. immitis and reported that the use of material from adult parasites had been unsuccessful.
Hyong-Sun et al. (in Canine Heartworm Disease, The Current Knowledge, Bradley and Pacheco, Eds, U. of Florida, Gainesville, 1972, pp. 55-67) utilized viable microfilaria as a possible vaccine for dog heartworm. They immunized dogs using seven vaccinations of microfilaria at three-day intervals into animals which were subsequently challenged with infectious larvae from laboratory-raised mosquitoes. The vaccinated animals showed microfilaria following challenge about two weeks after the unvaccinated controls and showed fewer microfilaria. However, this vaccination program showed that the viable microfilaria as a vaccine had little if any effect in altering the numbers of adult worms found in the vaccinated groups and the control groups which were not vaccinated.
Hyong-Sun et al. also attempted immunization of dogs with 15 kilorads (Kr) irradiated microfilaria but found that this level of irradiation was not lethal to all of the infectious larvae and, therefore, in the control groups so vaccinated but unchallenged, some of the dogs were ultimately found to have adult worms. The vaccine, therefore, was not effective.
Jovanovic, Acta Veterinaria 33(5-6):315-322 (1983), report attempts to vaccinate sheep against infection by D. filaria.
Sawada et al., Japan J. Expt. Med. 35(2): 125-132 (1965) (Chem. Abstr. 63: 16947), report isolation and purification of an antigen for an intradermal skin test. The antigen is extracted from a D. immitis homogenate with phosphate buffer (pH 7.2) and purified by a series of filtration and chromatographic procedures.
Boto et al., J. Immunol. 133(2): 975-980(1984), report analyses of D. immitis antigens prepared by detergent extraction (pH 7.4) of a D. immitis homogenate.
Maggio, European Patent Application No. (EP-A) 142,345, report published May 22, 1985, disclose use of anti-idiotypic monoclonal antibodies. Included in the disclosure are antibodies raised against a fraction of a D. immitis homogenate which is soluble at pH 3.5.
In Australian Patent Application No. 84-36-095 is disclosed a diagnostic assay employing an antibody raised against a D. immitis extract. The extract is prepared by extraction of an adult D. immitis homogenate with phosphate buffered saline at 4.degree. C. and filtering the supernatant thereof.
Swamy et al., Molec. Biochem. Parasit. 9:1 (1983), report isolated from two acid proteases from adult D. immitis extracts.
Grieve et al., Acta Tropica 42:63 (1985), report antigens which were solubilized from aqueous-insoluble material of adult female D. immitis with a detergent.